High performance facilitated transport membranes for olefin/paraffin separations

ABSTRACT

A high performance facilitated transport membrane comprising a metal cation exchanged/chelated carboxylic acid functional group containing functional polyimide, a method of making this a membrane, and the use of this membrane for olefin/paraffin separations, particularly for propylene/propane and ethylene/ethane separations. The facilitated transport membrane has either an asymmetric integrally skinned membrane structure or a thin film composite membrane structure, wherein the top selective layer of the membrane comprises a metal cation exchanged/chelated carboxylic acid functional group containing functional polyimide.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application No.62/357,213 filed Jun. 30, 2016, the contents of which cited applicationare hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Light olefins, such as propylene and ethylene, are produced asco-products from a variety of feed stocks in a number of differentprocesses in the chemical, petrochemical, and petroleum refiningindustries. Various petrochemical streams contain olefins and othersaturated hydrocarbons. Typically, these streams are from streamcracking units (ethylene production), catalytic cracking units (motorgasoline production), or the dehydrogenation of paraffins.

Currently, the separation of olefin and paraffin components is performedby cryogenic distillation, which is expensive and energy intensive dueto the low relative volatilities of the components. Large capitalexpense and energy costs have created incentives for extensive researchin this area of separations, and low energy-intensive membraneseparations have been considered as an attractive alternative.

In principle, membrane-based technologies have advantages of both lowcapital cost and high-energy efficiency compared to conventionalseparation methods for olefin/paraffin separations, such aspropylene/propane and ethylene/ethane separations. Four main types ofmembranes have been reported for olefin/paraffin separations includingfacilitated transport membranes, polymer membranes, mixed matrixmembranes, and inorganic membranes. Facilitated transport membranes, orion exchange membranes, which sometimes use silver ions as a complexingagent, have very high olefin/paraffin separation selectivity. However,poor chemical stability due to carrier poisoning or loss, high cost, andlow flux currently limit practical applications of facilitated transportmembranes.

Separation of olefins from paraffins via conventional polymer membraneshas not been commercially successful due to inadequate selectivities andpermeabilities of the polymeric membrane materials, as well asplasticization issues. Polymers that are more permeable are generallyless selective than are less permeable polymers. A general trade-offexists between permeability and selectivity of the polymeric membranematerials (the so-called “polymer upper bound limit”) for all kinds ofseparations, including olefin/paraffin separations. In recent years,substantial research effort has been directed to overcoming the limitsimposed by this upper bound. Various polymers and techniques have beenused, but without much success in terms of improving the membraneselectivity.

Much more efforts have been undertaken to develop metal ionincorporated, high olefin/paraffin selectivity facilitated transportmembranes. The high selectivity for olefin/paraffin is achieved by theincorporation of metal ions such as silver (I) or copper (I) cationsinto a solid nonporous polymer matrix layer on top of a highly porousmembrane support layer (so-called “fixed site carrier facilitatedtransport membrane”) or directly into the pores of the highly poroussupport membrane (so-called “supported liquid facilitated transportmembrane”) that results in the formation of a reversible metal cationcomplex with the pi bond of olefins, whereas no interaction occursbetween the metal cations and the paraffins. Addition of water,plasticizer, or humidification of the olefin/paraffin feed streams toeither the fixed site carrier facilitated transport membranes or thesupported liquid facilitated transport membranes is usually required toobtain reasonable olefin permeances and high olefin/paraffinselectivities. The performance of fixed site carrier facilitatedtransport membranes is much more stable than that of the supportedliquid facilitated transport membranes. The fixed site carrierfacilitated transport membranes are less sensitive to the loss of metalcation carriers than the supported liquid facilitated transportmembranes.

Pinnau et al. disclosed a solid polymer electrolyte fixed site carrierfacilitated transport membrane comprising silver tetrafluoroborateincorporated poly(ethylene oxide), see U.S. Pat. No. 5,670,051. Herreraet al. disclosed a process for the separation of olefin/paraffin using asilver cation-chelated chitosan fixed site carrier facilitated transportmembrane, see U.S. Pat. No. 7,361,800. Herrera et al. disclosed thecoating of a layer of chitosan on the surface of a microporous supportmembrane, wherein the support membrane is made from polyesters,polyamides, polyimides, polyvinylidene fluoride, polyacrylonitrile,polysulfones or polycarbonates. Common composite facilitated transportmembranes comprise ultrafiltration or microfiltration membrane as thesupport membrane.

Feiring et al. disclosed a new facilitated transport membrane comprisingsilver (I) cation exchanged fluorinated copolymer synthesized from aperfluorinated cyclic or cyclizable monomer and a strong acid highlyfluorinated vinylether compound. The membrane, however, did not showolefin to paraffin selectivity higher than 200, see US 2015/0025293.

The composite facilitated transport membranes disclosed in theliterature comprise an ultrafiltration or microfiltration membrane asthe support membrane. The use of a relatively hydrophilic, nanoporouspolymeric membrane such as polyethersulfone membrane as the supportmembrane for the preparation of fixed site carrier facilitated transportmembranes for olefin/paraffin separations has not been reported in theliterature. In particular, the use of a relatively hydrophilic, verysmall pore, nanoporous support membrane with an average pore diameter ofless than 10 nm on the membrane skin layer surface for the preparationof fixed site carrier facilitated transport membranes has not beendisclosed in the literature.

Development of new stable, high permeance, and high selectivityfacilitated transport membranes is critical for the future success inthe use of membranes for olefin/paraffin separations such aspropylene/propane separation.

SUMMARY OF THE INVENTION

This invention discloses a new high performance facilitated transportmembrane comprising a carboxylic acid functional group containingpolyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations, a method of making such a membrane, and the use ofsuch a membrane for olefin/paraffin separations, particularly forpropylene/propane (C3=/C3) and ethylene/ethane (C2=/C2) separations.

The new high performance facilitated transport membrane disclosed in thepresent invention comprises a carboxylic acid functional groupcontaining polyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations. The new high performance facilitated transportmembrane disclosed in the present invention has either an asymmetricintegrally skinned membrane structure or a thin film composite membranestructure, wherein at least the top selective layer of the membranecomprises a carboxylic acid functional group containing polyimide, andwherein the carboxylic acid functional groups are ion-exchanged orchelated with metal cations such as silver (I) or cupper (I) cations.Different from the facilitated transport membranes reported by Pinnau etal. (U.S. Pat. No. 5,670,051), Herrera et al. (U.S. Pat. No. 7,361,800),Feiring et al. (US 2015/0025293), the current invention discloses a newhigh performance facilitated transport membrane comprising a carboxylicacid functional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations to form said facilitated transportmembrane with stable separation performance. The present inventionteaches the use of carboxylic acid functional group containing polyimidefor the preparation of the new facilitated transport membrane forolefin/paraffin separation. The use of a polyimide comprising carboxylicacid functional groups in the present invention is to stabilize themetal cations in the new high performance facilitated transport membraneand also to provide asymmetric integrally skinned or thin film compositemembrane structure. The polyimide comprising carboxylic acid functionalgroups can be easily fabricated into asymmetric membranes. Thecarboxylic acid functional groups on the polyimide can be ion-exchangedor chelated with the metal cations such as silver (I) cations to formthe facilitated transport membrane with stable separation performance.

The facilitated transport membranes comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations described in the current inventionshowed high olefin/paraffin selectivity, high olefin permeance, andstable performance over time. The high selectivity and high permeance ofthe facilitated transport membranes described in the current inventionis achieved by the formation of a reversible metal cation complex withthe pi bond of olefins, whereas no interaction occurs between the metalcations and the paraffins.

One new high performance facilitated transport membrane 1.5MAg+/PI-50described in the present invention with an asymmetric integrally skinnedflat sheet membrane structure was fabricated from carboxylic acidcontaining poly(2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropanedianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimide (abbreviated asPI-50) that was synthesized from 2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and a mixture of 3,5-diaminobenzoicacid (3,5-DBA) and 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) (molarratio of 3,5-DBA/HAB=1:4), wherein the carboxylic acid functional groupson PI-50 were ion-exchanged or chelated with silver (I) cation.Permeation testing experiments using humidified (relative humidity80-100%) propylene and propane mixed vapor phase feed (30% propylene and70% propane at 791 kPa (100 psig) and 35° C.) showed that this1.5MAg+/PI-50 membrane had both high propylene (C3=) permeance(P_(C3=)/L=259 GPU) and high propylene/propane (C3=/C3) selectivity(α_(C3=/C3)=466). Permeation testing experiments using humidified(relative humidity 80-100%) propylene and propane mixed vapor phase feed(70% propylene and 30% propane at 791 kPa (100 psig) and 35° C.) alsoshowed that this 1.5MAg+/PI-50 membrane had both high propylene (C3=)permeance (P_(C3=)/L=192 GPU) and high propylene/propane (C3=/C3)selectivity (α_(C3=/C3)=˜1000).

Another new high performance facilitated transport membrane 3MAg+/PI-150described in the present invention with an asymmetric integrally skinnedmembrane flat sheet structure was fabricated from carboxylic acidcontaining poly(2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropanedianhydride-3,5-diaminobenzoic acid-3,3′,5,5′-tetramethyl-4,4′-methylenedianiline) polyimide (abbreviated as PI-150) derived from thepolycondensation reaction of 6FDA and a mixture of 3,5-DBA and3,3′,5,5′-tetramethyl-4,4′-methylene dianiline (TMMDA) (molar ratio of3,5-DBA/TMMDA=2:1), wherein the carboxylic acid functional groups onPI-150 were ion-exchanged or chelated with silver cation. Permeationtesting experiments using humidified (relative humidity 80-100%)propylene and propane mixed vapor phase feed (30% propylene and 70%propane at 791 kPa (100 psig) and 35° C.) showed that this 3MAg+/PI-150membrane has both high propylene (C3=) permeance (P_(C3=)/L=147 GPU) andhigh propylene/propane (C3=/C3) selectivity (α_(C3=/C3)=239).

The new high performance facilitated transport membrane comprising acarboxylic acid functional group containing polyimide wherein thecarboxylic acid functional groups are ion-exchanged or chelated withmetal cations such as silver (I) or copper (I) cations disclosed in thepresent invention also showed much more stable membrane performance thanthe metal cation impregnated asymmetric polymeric facilitated transportmembranes without any carboxylic acid functional groups such as silver(I) cation impregnated asymmetric polyethersulfone membrane with silver(I) cation impregnated in the top selective layer of the membrane.

The present invention also discloses a method of making the new highperformance facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver or copper (I) cations. The method comprises: 1) preparation ofan asymmetric carboxylic acid functional group containing a polyimideflat sheet or a hollow fiber membrane with either an asymmetricintegrally skinned or a thin film composite membrane structure, whereinat least the top selective layer of the membrane comprises a carboxylicacid functional group containing polyimide; 2) preparation of thefacilitated transport membrane by ion-exchanging or chelating thecarboxylic acid functional groups on the polyimide polymer of theasymmetric carboxylic acid functional group containing the polyimideflat sheet or the hollow fiber membrane prepared in step 1) with metalcations such as silver (I) or copper (I) cations. The top selectivelayer surface of the asymmetric carboxylic acid functional groupcontaining the polyimide flat sheet or hollow fiber membrane prepared instep 1) was soaked in a metal cation aqueous solution such as silvernitrate (AgNO₃) aqueous solution for a sufficient time to form thefacilitated transport membrane comprising metal cation ion-exchanged orchelated carboxylic acid functional group containing polyimide.

The present invention provides a process for separating olefin from amixture of olefin and paraffin using the new high performancefacilitated transport membrane comprising a carboxylic acid functionalgroup containing polyimide wherein the carboxylic acid functional groupsare ion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations described in the present invention, the processcomprising: (a) providing a new high performance facilitated transportmembrane comprising a carboxylic acid functional group containingpolyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations described in the present invention which is permeableto said olefin; (b) contacting the humidified olefin/paraffin mixturefeed on one side of the new high performance facilitated transportmembrane comprising a carboxylic acid functional group containingpolyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations described in the present invention to cause saidolefin to permeate the membrane; and (c) removing from the opposite sideof the membrane a permeate gas composition comprising a portion of saidolefin which permeated through said membrane.

DETAILED DESCRIPTION OF THE INVENTION

Membrane technology has been of great interest for the separation ofolefin/paraffin mixtures. However, despite significant research efforton olefin/paraffin separations by membrane technology, no commercialolefin/paraffin separation application using membranes has beenreported.

The present invention discloses a new high performance facilitatedtransport membrane comprising a carboxylic acid functional groupcontaining polyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations, The present invention further discloses a method ofmaking such a membrane and the use of such a membrane forolefin/paraffin separations, particularly for propylene/propane (C3=/C3)and ethylene/ethane (C2=/C2) separations.

The new high performance facilitated transport membrane disclosed in thepresent invention comprises a carboxylic acid functional groupcontaining polyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations. The metal cation ion-exchanged or chelatedcarboxylic acid functional group containing polyimide described in thecurrent invention comprising a plurality of repeating units of formula(I)

wherein X₁ and X₂ are selected from the group consisting of

and mixtures thereof, and wherein X1 and X2 may be the same or differentfrom each other;wherein Y₁—COOM is selected from the group consisting of

and mixtures thereof and wherein M is selected from silver (I) cation orcopper (I) cation;wherein Y2 is selected from the group consisting of

and mixtures thereof, and —R′— is selected from the group consisting of

and mixtures thereof, and —R″— is selected from the group consisting of—H, COCH₃, and mixtures thereof, and M is selected from silver (I)cation or copper (I) cation; wherein n and m are independent integersfrom 2 to 500; and wherein n/m is in a range of 1:0 to 1:10, andpreferably n/m is in a range of 1:0 to 1:5.

Preferably, X₁ and X₂ are selected from the group consisting of

and mixtures thereof, and wherein X1 and X2 may be the same or differentfrom each other; preferably Y₁—COOM is selected from the groupconsisting of

and mixtures thereof; preferably Y2 is selected from the groupconsisting of

and mixtures thereof.

The carboxylic acid functional group containing polyimide used for thepreparation the new high performance facilitated transport membranecomprising a carboxylic acid functional group containing polyimidewherein the carboxylic acid functional groups are ion-exchanged orchelated with metal cations such as silver (I) or copper (I) cationsdescribed in the current invention comprising a plurality of repeatingunits of formula (II)

wherein X₁ and X₂ are selected from the group consisting of

and mixtures thereof, and wherein X1 and X2 may be the same or differentfrom each other;wherein Y₁—COOH is selected from the group consisting of

and mixtures thereof; wherein Y2 is selected from the group consistingof

and mixtures thereof, and —R′— is selected from the group consisting of

and mixtures thereof, and —R″— is selected from the group consisting of—H, COCH₃, and mixtures thereof; wherein n and m are independentintegers from 2 to 500; and wherein n/m is in a range of 1:0 to 1:10,and preferably n/m is in a range of 1:0 to 1:5.

Preferably, X₁ and X₂ are selected from the group consisting of

and mixtures thereof, and wherein X1 and X2 may be the same or differentfrom each other; preferably Y₁—COOH is selected from the groupconsisting of

and mixtures thereof; preferably Y2 is selected from the groupconsisting of

and mixtures thereof, and —R″— is selected from the group consisting of—H, COCH₃, and mixtures thereof.

The carboxylic acid functional group containing polyimide comprising aplurality of repeating units of formula (II) used for the preparationthe new high performance facilitated transport membrane comprising acarboxylic acid functional group containing polyimide wherein thecarboxylic acid functional groups are ion-exchanged or chelated withmetal cations such as silver (I) or copper (I) cations of the inventionmay be selected from, but is not limited to, the group consisting ofpoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimides derived from apolycondensation reaction of2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) witha mixture of 3,5-diaminobenzoic acid (3,5-DBA) and3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and the molar ratio of3,5-DBA to HAB may be in a range of 1:0 to 1:5,poly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoic acid-3,3′,5,5′-tetramethyl-4,4′-methylenedianiline) polyimides derived from the polycondensation reaction of 6FDAand a mixture of 3,5-DBA and 3,3′,5,5′-tetramethyl-4,4′-methylenedianiline (TMMDA) and the molar ratio of 3,5-DBA to TMMDA may be in arange of 1:0 to 1:5, poly(6FDA-3,5-DBA),poly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,3′-methylenebis(6-aminobenzoicacid)-3,3′,5,5′-tetramethyl-4,4′-methylene dianiline) polyimides derivedfrom the polycondensation reaction of 6FDA and a mixture of3,3′-methylenebis(6-aminobenzoic acid) (MBA) and TMMDA and the molarratio of MBA to TMMDA may be in a range of 1:0 to 1:5, poly(6FDA-MBA),poly(6FDA-MBA-HAB)s and the molar ratio of MBA to HAB may be in a rangeof 1:0 to 1:5, poly(3,3′,4,4′-diphenylsulfone tetracarboxylicdianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimides derived from apolycondensation reaction of 3,3′,4,4′-diphenylsulfone tetracarboxylicdianhydride (DSDA) with a mixture of 3,5-DBA and HAB and the molar ratioof 3,5-DBA to HAB may be in a range of 1:0 to 1:5,poly(DSDA-3,5-DBA-TMMDA)s and the molar ratio of 3,5-DBA to TMMDA may bein a range of 1:0 to 1:5, poly(DSDA-MBA-TMMDA)s and the molar ratio ofMBA to TMMDA may be in a range of 1:0 to 1:5, poly(DSDA-MBA-HAB)s andthe molar ratio of MBA to HAB may be in a range of 1:0 to 1:5,poly(DSDA-3,5-DBA), poly(DSDA-MBA), poly(DSDA-3,5-DBA-MBA)s and themolar ratio of 3,5-DBA to MBA may be in a range of 1:0 to 1:5,poly(3,3′,4,4′-diphenylsulfone tetracarboxylicdianhydride-3,4-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimides derived from apolycondensation reaction of DSDA with a mixture of 3,4-DBA and HAB andthe molar ratio of 3,4-DBA to HAB may be in a range of 1:0 to 1:5,poly(6FDA-3,4-DBA-HAB)s and the molar ratio of 3,4-DBA to HAB may be ina range of 1:0 to 1:5, poly(3,3′,4,4′-benzophenone tetracarboxylicdianhydride-pyromellitic dianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimides derived from apolycondensation reaction of a mixture of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA)with a mixture of 3,5-DBA and HAB and the molar ratio of 3,5-DBA to HABmay be in a range of 1:0 to 1:5 and the molar ratio of BTDA to PMDA maybe in a range of 2:1 to 1:2, poly(BTDA-PMDA-MBA-HAB)s and the molarratio of MBA to HAB may be in a range of 1:0 to 1:5 and the molar ratioof BTDA to PMDA may be in a range of 2:1 to 1:2,poly(BTDA-PMDA-MBA-TMMDA)s and the molar ratio of MBA to TMMDA may be ina range of 1:0 to 1:5 and the molar ratio of BTDA to PMDA may be in arange of 2:1 to 1:2, poly(BTDA-PMDA-3,5-DBA-TMMDA)s and the molar ratioof 3,5-DBA to TMMDA may be in a range of 1:0 to 1:5 and the molar ratioof BTDA to PMDA may be in a range of 2:1 to 1:2, and blends thereof.

The new high performance facilitated transport membrane disclosed in thepresent invention has either an asymmetric integrally skinned membranestructure or a thin film composite membrane structure, wherein at leastthe top selective layer of the membrane comprises a carboxylic acidfunctional group containing polyimide, and wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver or copper (I) cations. Both the top selective layer and thehighly porous support layer underneath the top selective layer of theasymmetric integrally skinned facilitated transport membranes disclosedin the present invention comprise a carboxylic acid functional groupcontaining polyimide, and wherein the carboxylic acid functional groupsare ion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations. The asymmetric integrally skinned membranescomprising a carboxylic acid functional group containing polyimide forthe preparation of the high performance facilitated transport membranesdisclosed in the present invention are fabricated via a phase inversiontechnique.

The facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations described in the present inventioncan be fabricated into any convenient form suitable for a desiredapplication. For example, the membranes can be in the form of hollowfibers, tubes, flat sheets, and the like. The membranes can also be inthe form of thin film composite comprising a carboxylic acid functionalgroup containing polyimide selective layer wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations and a porous supporting layercomprising a polymer material different from the carboxylic acidfunctional group containing polyimide described in the current inventionor an inorganic material. The form of the membrane may depend upon thenature of the membrane itself and the ease of manufacturing the form.The membrane can be assembled in a separator in any suitableconfiguration for the form of the membrane and the separator may providefor co-current, counter-current, or cross-current flows of the feed onthe retentate and permeate sides of the membrane. In one exemplaryembodiment a facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations for olefin/paraffin separations in aspiral wound module is in the form of flat sheet having a thickness fromabout 30 to about 400 μm. In another exemplary embodiment a facilitatedtransport membrane comprising a carboxylic acid functional groupcontaining polyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations for olefin/paraffin separations is in a hollow fibermodule that is in the form of thousands, tens of thousands, hundreds ofthousands, or more, of parallel, closely-packed hollow fibers or tubes.In one embodiment, each fiber has an outside diameter of from about 200micrometers (μm) to about 700 millimeters (mm) and a wall thickness offrom about 30 to about 200 μm. In operation, a feed contacts a firstsurface of the membrane, a permeate permeates the membrane and isremoved therefrom, and a retentate, not having permeated the membrane,also is removed therefrom. In another embodiment, a facilitatedtransport membrane comprising a carboxylic acid functional groupcontaining polyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations for olefin/paraffin separations can be in the form offlat sheet having a thickness in the range of from about 30 to about 400μm.

Different from the facilitated transport membranes reported by Pinnau etal. (U.S. Pat. No. 5,670,051), Herrera et al. (U.S. Pat. No. 7,361,800),Feiring et al. (US 2015/0025293), the current invention discloses a newhigh performance facilitated transport membrane comprising a carboxylicacid functional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations to form said facilitated transportmembrane with stable separation performance. The present inventionteaches the use of carboxylic acid functional group containing polyimidefor the preparation of the new facilitated transport membrane forolefin/paraffin separation. The use of polyimide comprising carboxylicacid functional groups in the present invention is to stabilize themetal cations in the new high performance facilitated transport membraneand also to provide asymmetric integrally skinned or thin film compositemembrane structure. The polyimide comprising carboxylic acid functionalgroups in the present invention can be easily fabricated into asymmetricmembranes. The carboxylic acid functional groups on the polyimide can beion-exchanged or chelated with the metal cations such as silver cationto form said facilitated transport membrane with stable separationperformance.

The facilitated transport membranes comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations described in the current inventionshowed high olefin/paraffin selectivity, high olefin permeance, andstable performance over time. The high selectivity and high permeance ofthe facilitated transport membranes described in the current inventionis achieved by the formation of a reversible metal cation complex withthe pi bond of olefins, whereas no interaction occurs between the metalcations and the paraffins.

The new high performance facilitated transport membrane comprising acarboxylic acid functional group containing polyimide wherein thecarboxylic acid functional groups are ion-exchanged or chelated withmetal cations such as silver (I) or copper (I) cations disclosed in thepresent invention also showed much more stable membrane performance thanthe metal cation impregnated asymmetric polymeric facilitated transportmembranes without any carboxylic acid functional groups such as silvercation impregnated asymmetric polyethersulfone membrane with silvercation impregnated in the top selective layer of the membrane.

The present invention also discloses a method of making the new highperformance facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations. The method comprises: 1)Preparation of asymmetric carboxylic acid functional group containingpolyimide flat sheet or hollow fiber membrane with either asymmetricintegrally skinned or thin film composite membrane structure, wherein atleast the top selective layer of said membrane comprises a carboxylicacid functional group containing polyimide; 2) Preparation of thefacilitated transport membrane by ion-exchanging or chelating thecarboxylic acid functional groups on the polyimide polymer of saidasymmetric carboxylic acid functional group containing polyimide flatsheet or hollow fiber membrane prepared in step 1) with metal cationssuch as silver (I) or copper (I) cations. The top selective layersurface of said asymmetric carboxylic acid functional group containingpolyimide flat sheet or hollow fiber membrane prepared in step 1) wassoaked in a metal cation aqueous solution such as silver nitrate (AgNO₃)aqueous solution for a certain time to form the facilitated transportmembrane comprising metal cation ion-exchanged or chelated carboxylicacid functional group containing polyimide.

The present invention provides a process for the separation of paraffinand olefin, such as, for example, in gaseous streams produced fromstream cracking, catalytic cracking, the dehydration of paraffins, andthe like using the new high performance facilitated transport membranecomprising a carboxylic acid functional group containing polyimidewherein the carboxylic acid functional groups are ion-exchanged orchelated with metal cations such as silver (I) or copper (I) cationsdescribed in the present invention, and the process comprises: (a)providing a new high performance facilitated transport membranecomprising a carboxylic acid functional group containing polyimidewherein the carboxylic acid functional groups are ion-exchanged orchelated with metal cations such as silver (I) or copper (I) cationsdescribed in the present invention which is permeable to said olefin;(b) contacting the humidified olefin/paraffin mixture feed on one sideof the new high performance facilitated transport membrane comprising acarboxylic acid functional group containing polyimide wherein thecarboxylic acid functional groups are ion-exchanged or chelated withmetal cations such as silver (I) or copper (I) cations described in thepresent invention to cause said olefin to permeate the membrane; and (c)removing from the opposite side of the membrane a permeate gascomposition comprising a portion of said olefin which permeated throughsaid membrane. The process utilizes a facilitated transport membranecomprising a carboxylic acid functional group containing polyimidewherein the carboxylic acid functional groups are ion-exchanged orchelated with metal cations such as silver (I) or copper (I) cationsdescribed in the present invention that is highly permeable but alsohighly selective to olefin, thus permitting olefin to permeate themembrane at a much higher rate than the paraffin. The membrane can takea variety of forms suitable for a particular application. For example,the membrane can be in the form of a flat sheet, hollow tube or fiber,and the like. In this regard, various embodiments of the processcontemplated herein can be used to replace C2 and C3 splitters, ashybrid membrane distillation units for olefin purification, for recoveryof olefins from polypropylene vent streams or from fluid catalyticcracking (FCC) off-gas streams, or the like. The process can also beused for the production of polymer grade propylene, thus offeringsignificant energy, capital, and operating cost savings compared toconventional distillation.

The olefin/paraffin separation process using the facilitated transportmembrane comprising a carboxylic acid functional group containingpolyimide wherein the carboxylic acid functional groups areion-exchanged or chelated with metal cations such as silver (I) orcopper (I) cations starts by contacting a first surface of the membranewith an olefin/paraffin feed. The olefin may comprise, for example,propylene or ethylene and the paraffin may comprise propane or ethane,respectively. The olefin/paraffin feed comprises a first concentrationof olefin and a first concentration of paraffin depending on theapplication for which the membrane separation is used. For example, apropane dehydrogenation process typically provides a feed containingabout 35 mass percent propylene, whereas a feed from an FCC unitgenerally contains about 75 mass percent propylene. The flow rate andtemperature of the olefin/paraffin feed have those values that aresuitable for a desired application. Next, a permeate is caused to flowthrough the membrane and from a second surface of the membrane. Becausethe facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations for olefin/paraffin separations ismuch more selective to the olefin than to the paraffin, the permeate hasa concentration of olefin that is higher than the concentration of theolefin in the feed. In one exemplary embodiment, the concentration ofthe olefin in the permeate is 99.5 mass percent. In addition, while someparaffin may permeate through the membrane, the permeate has aconcentration of paraffin that is less than the concentration of theparaffin in the feed. The permeate can then be removed from the secondsurface of the membrane. As the permeate passes through the membrane, aretentate or residue, which has not permeated the membrane, is removedfrom the first surface of the membrane. The retentate has aconcentration of olefin that is lower than the concentration of olefinin the feed and lower than the concentration of the permeate. Theretentate also has a concentration of paraffin that is higher than aconcentration of paraffin that is in the feed.

EXAMPLES

The following examples are provided to illustrate one or more preferredembodiments of the invention, but are not limited embodiments thereof.Numerous variations can be made to the following examples that liewithin the scope of the invention.

Example 1 Preparation of Silver (I) Cation Exchanged/ChelatedPoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoic acid-3,3′,5,5′-tetramethyl-4,4′-methylenedianiline) Polyimide Facilitated Transport Membrane 1) Synthesis ofCarboxylic Acid Containingpoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoic acid-3,3′,5,5′-tetramethyl-4,4′-methylenedianiline) polyimide (Abbreviated as PI-150) Polyimide

The aromatic carboxylic acid containingpoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoic acid-3,3′,5,5′-tetramethyl-4,4′-methylenedianiline) polyimide (abbreviated as PI-150) was synthesized from2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and amixture of 3,5-diaminobenzoic acid (3,5-DBA) and3,3′,5,5′-tetramethyl-4,4′-methylene dianiline (TMMDA) (molar ratio of3,5-DBA/TMMDA=2:1) in dimethylacetamide (DMAc) polar solvent by atwo-step process involving the formation of the poly(amic acid) followedby a solution imidization process. Acetic anhydride was used as thedehydrating agent and pyridine was used as the imidization catalyst forthe solution imidization reaction. For example, a 250 mL three-neckround-bottom flask equipped with a nitrogen inlet and a mechanicalstirrer was charged with 9.0 g of 3,5-DBA, 7.6 g of TMMDA and 36.2 g ofDMAc. Once 3,5-DBA and TMMDA monomers were fully dissolved, 41.2 g of6FDA solid powder was added to the solution of 3,5-DBA and TMMDAstepwise under stirring in the flask. 155 g of DMAc was added to thesolution after the 6FDA powder was added. The reaction mixture wasmechanically stirred for 24 hours at ambient temperature to give aviscous poly(amic acid) solution. Then 20.8 g of acetic anhydride wasadded slowly to the reaction mixture under stirring followed by theaddition of 30.8 g of pyridine to the reaction mixture. The reactionmixture was mechanically stirred for an additional 2.0 hours at 90° C.to yield a polyimide designated as PI-150 for the purpose of thisapplication. The PI-150 product in a fine fiber form was recovered byslowly precipitating the reaction mixture into a large amount ofmethanol and water mixture. The resultant PI-150 polyimide fibers werethen thoroughly rinsed with methanol and dried in a vacuum oven at 200°C. for 48 hours.

2) Fabrication of Asymmetric Integrally Skinned PI-150 Membrane

A PI-150 membrane casting dope containing PI-150 polyimide synthesizedin step 1), NMP, 1,3-dioxolane, glycerol and n-decane was cast on ahighly porous non-selective symmetric woven Nylon 6,6 fabric backing ata casting speed of 4 fpm at room temperature. The cast membrane wasevaporated for 20 seconds to form the nascent asymmetricintegrally-skinned flat sheet PI-150 membrane. The membrane was immersedinto a cold water coagulation tank and then immersed into a hot watertank to remove the trace amount of organic solvents in the membrane.Finally the wet membrane was wound up on a core roll.

3) Preparation of 3MAg+/PI-150 Facilitated Transport Membrane

The skin layer surface of the wet PI-150 membrane was immersed in a 3MAgNO₃ aqueous solution for 2.5 h and then the AgNO₃ aqueous solution wasremoved from the membrane surface to form the Ag+ exchanged/chelatedPI-150 facilitated transport membrane (abbreviated as 3MAg+/PI-150 for3M AgNO₃ aqueous solution treated PI-150 membrane).

Example 2 Preparation of Silver (I) Cation Exchanged/ChelatedPoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) Polyimide FacilitatedTransport Membranes 1) Synthesis of Carboxylic Acid Containingpoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) Polyimide (abbreviated asPI-50) Polyimide

The aromatic carboxylic acid containingpoly(2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropanedianhydride-3,5-diaminobenzoicacid-3,3′-dihydroxy-4,4′-diamino-biphenyl) polyimide (abbreviated asPI-50) was synthesized from 6FDA and a mixture 3,5-DBA and3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) (molar ratio of3,5-DBA/HAB=1:4) in dimethylacetamide (DMAc) polar solvent by a two-stepprocess involving the formation of the poly(amic acid) followed by asolution imidization process. Acetic anhydride was used as thedehydrating agent and pyridine was used as the imidization catalyst forthe solution imidization reaction. For example, a 1 L three-neckround-bottom flask equipped with a nitrogen inlet and a mechanicalstirrer was charged with 9.1 g of 3,5-DBA, 51.9 g of HAB and 660 g ofDMAc. Once 3,5-DBA and HAB monomers were fully dissolved, 133.9 g of6FDA solid powder was added to the solution of 3,5-DBA and HAB stepwiseunder stirring in the flask. 445 g of DMAc was added to the solutionafter the 6FDA powder was added. The reaction mixture was mechanicallystirred for 24 hours at ambient temperature to give a viscous poly(amicacid) solution. Then 72.0 g of acetic anhydride was added slowly to thereaction mixture under stirring followed by the addition of 104.4 g ofpyridine to the reaction mixture. The reaction mixture was mechanicallystirred for an additional 2.5 hours at 90° C. to yield a polyimidedesignated as PI-50 for the purpose of this application. The PI-50product in a fine fiber form was recovered by slowly precipitating thereaction mixture into a large amount of methanol and water mixture. Theresultant PI-50 polyimide fibers were then thoroughly rinsed withmethanol and dried in a vacuum oven at 120° C. for 48 hours.

2) Fabrication of Asymmetric Integrally Skinned PI-50 Membrane

A PI-50 membrane casting dope containing PI-50 polyimide synthesized instep 1), NMP, 1,3-dioxolane, glycerol and n-decane was cast on a highlyporous non-selective symmetric woven Nylon 6,6 fabric backing at acasting speed of 4 fpm at room temperature. The cast membrane wasevaporated for 20 seconds to form the nascent asymmetricintegrally-skinned flat sheet PI-50 membrane. The membrane was immersedinto a cold water coagulation tank and then immersed into a hot watertank to remove the trace amount of organic solvents in the membrane.Finally the wet membrane was wound up on a core roll.

3) Preparation of Ag+/PI-50 Facilitated Transport Membranes

The skin layer surface of the wet PI-50 membrane was immersed in a 1M,1.5M or 3M AgNO₃ aqueous solution for 2.5 h and then the AgNO₃ aqueoussolution was removed from the membrane surface to form the Ag+exchanged/chelated PI-50 facilitated transport membranes (abbreviated as1MAg+/PI-50 for 1.0M AgNO₃ aqueous solution treated PI-50 membrane,1.5MAg+/PI-50 for 1.5M AgNO₃ aqueous solution treated PI-50 membrane,and 3MAg+/PI-50 for 3M AgNO₃ aqueous solution treated PI-50 membrane).

Comparative Example 1 Preparation of Silver (I) Cation ImpregnatedPolyethersulfone Facilitated Transport Membrane 1) Fabrication ofAsymmetric Integrally Skinned Polyethersulfone (PES) Membrane

A PES membrane casting dope containing PES, NMP, 1,3-dioxolane, glyceroland n-decane was cast on a highly porous non-selective symmetric wovenNylon 6,6 fabric backing at a casting speed of 6 fpm at roomtemperature. The cast membrane was evaporated for 13 seconds to form thenascent asymmetric integrally-skinned flat sheet PES membrane. Themembrane was immersed into a cold water coagulation tank and thenimmersed into a hot water tank to remove the trace amount of organicsolvents in the membrane. Finally the wet membrane was wound up on acore roll.

2) Preparation of 3MAg+/PES Facilitated Transport Membrane

The skin layer surface of the wet asymmetric integrally skinned PESmembrane was immersed in a 3M AgNO₃ aqueous solution for 2.5 h and thenthe AgNO₃ aqueous solution was removed from the membrane surface to formthe Ag+ impregnated PES facilitated transport membrane (abbreviated as3MAg+/PES for 3M AgNO₃ aqueous solution treated PES membrane).

Example 3 Evaluation of Propylene/Propane Separation Performance of theFacilitated Transport Membranes

The 3MAg+/PI-150, 3MAg+/PI-50, and 3MAg+/PES facilitated transportmembranes were evaluated for propylene/propane separation at 35° C.under 791 kPa (100 psig) propylene/propane (30%/70%) mixed vapor phasefeed pressure wherein the feed stream was bubbled through water at 35°C. The retentate flow rate was set at 708 scc/min. The results in Table1 show that the new 3MAg+/PI-150 and 3MAg+/PI-50 facilitated transportmembranes disclosed in the present invention have both high propylene(C3=) permeance of ≥145-199 GPU and high propylene/propane (C3=/C3)selectivity of 239-307. The propylene/propane permeation experimentsalso demonstrated that the new 3MAg+/PI-150 and 3MAg+/PI-50 facilitatedtransport membranes comprising carboxylic acid functional groupsion-exchanged or chelated with silver (I) cations disclosed in thepresent invention showed much more stable membrane performance than thecomparative 3MAg+/PES facilitated transport membrane without anycarboxylic acid functional groups. The comparative 3MAg+/PES facilitatedtransport membrane showed Knudsen flow without any propylene/propaneselectivity under 791 kPa (100 psig) propylene/propane (30%/70%) mixedvapor phase feed pressure.

TABLE 1 Propylene/propane permeation test results of 3 MAg+/PI-150, 3MAg+/PI-50, and 3 MAg+/PES facilitated transport membranes^(a) MembraneP_(C3=)/L (GPU) α_(C3=/C3)  3 MAg+/PI-150 146.5 239 3 MAg+/PI-50 198.9307 3 MAg+/PES  overflow ~1 ^(a)Tested at 35° C., 790 kPa (100 psig)propylene/propane (30%/70%) mixed vapor feed pressure; feed stream wasbubbled through water at 35° C.; retentate flow rate was set at 708scc/min; data collected after 1 h of testing; 1 GPU = 10⁻⁶ cm³ (STP)/cm²s (cm Hg).

Example 4 Evaluation of 1MAg+/PI-50, 1.5MAg+/PI-50, 3MAg+/PI-50Facilitated Transport Membranes with Different Silver (I) CationContents for Propylene/Propane Separation

The 1MAg+/PI-50, 1.5MAg+/PI-50, 3MAg+/PI-50 facilitated transportmembranes with different silver (I) cation content disclosed in thepresent invention were evaluated for propylene/propane separation at 35°C. under 791 kPa (100 psig) propylene/propane (30%/70%) mixed vaporphase feed pressure wherein the feed stream was bubbled through water at35° C. The retentate flow rate was set at 708 scc/min. The results inTable 2 show that the 1.5MAg+/PI-50 facilitated transport membraneprepared from 1.5M AgNO₃ aqueous solution exhibits the highestpropylene/propane selectivity and propylene permeance among the threemembranes. The results in Table 2 show that the 1.5MAg+/PI-50facilitated transport membrane prepared from 1.5M AgNO₃ aqueous solutionalso exhibits high propylene/propane selectivity and propylene permeancewith a high propylene concentration feed of 70% propylene and 30%propane.

TABLE 2 Propylene/propane permeation test results of 1 MAg+/PI-50, 1.5MAg+/PI-50, and 3 MAg+/PI-50 facilitated transport membranes MembraneP_(C3=)/L (GPU) α_(C3=/C3) 1 MAg+/PI-50 ^(a) 278.3 285 1.5 MAg+/PI-50^(a ) 258.6 466 1.5 MAg+/PI-50 ^(b ) 191.5 ~1000 3 MAg+/PI-50 ^(a) 198.9307 ^(a) Tested at 35° C., 790 kPa (100 psig) propylene/propane(30%/70%) mixed vapor feed pressure; feed stream was bubbled throughwater at 35° C.; retentate flow rate was set at 708 scc/min; datacollected after 1 h of testing; ^(b) Tested at 35° C., 790 kPa (100psig) propylene/propane (70%/30%) mixed vapor feed pressure; feed streamwas bubbled through water at 35° C.; retentate flow rate was set at 708scc/min; data collected after 1 h of testing; 1 GPU = 10⁻⁶ cm³ (STP)/cm²s (cm Hg).

Specific Embodiments

While the following is described in conjunction with specificembodiments, it will be understood that this description is intended toillustrate and not limit the scope of the preceding description and theappended claims.

A first embodiment of the invention is a facilitated transport membranecomprising a carboxylic acid functional group containing polyimidewherein the carboxylic acid functional groups are ion-exchanged orchelated with silver (I) or copper (I) cations wherein the silver (I) orcopper (I) cation ion-exchanged or chelated carboxylic acid functionalgroup containing polyimide comprises a plurality of repeating units offormula (I)

wherein X₁ and X₂ are selected from the group consisting of

and mixtures thereof, wherein X1 and X2 may be the same or differentfrom each other; wherein Y₁—COOM is selected from the group consistingof

and mixtures thereof and wherein M is selected from a silver cation or acopper (I) cation;wherein Y2 is selected from the group consisting of

and mixtures thereof, —R′— is selected from the group consisting of

and mixtures thereof, —R″— is selected from the group consisting of —H,COCH₃, and mixtures thereof, M is selected from a silver (I) cation or acopper (I) cation; wherein n and m are independent integers from 2 to500; and wherein n/m is in a range of 1:0 to 1:10. An embodiment of theinvention is one, any or all of prior embodiments in this paragraph upthrough the first embodiment in this paragraph wherein X₁ and X₂ areselected from the group consisting of

and mixtures thereof. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph wherein Y₁—COOM is selected from the group consistingof

and mixtures thereof. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph wherein Y2 is selected from the group consisting of

and mixtures thereof. An embodiment of the invention is one, any or allof prior embodiments in this paragraph up through the first embodimentin this paragraph wherein —R″— is selected from the group consisting of—H, COCH₃, and mixtures thereof.

A second embodiment of the invention is a method of making a highperformance facilitated transport membrane comprising a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with metal cations suchas silver (I) or copper (I) cations, the method comprising a) preparingan asymmetric carboxylic acid functional group containing polyimide flatsheet or hollow fiber membrane with either an asymmetric integrallyskinned or a thin film composite membrane structure, wherein at leastthe top selective layer of the membrane comprises a carboxylic acidfunctional group containing polyimide; and b) preparation thefacilitated transport membrane by ion-exchanging or chelating thecarboxylic acid functional groups on the polyimide polymer of theasymmetric carboxylic acid functional group containing polyimide flatsheet or hollow fiber membrane prepared in step a) with silver (I) orcopper (I) cations. An embodiment of the invention is one, any or all ofprior embodiments in this paragraph up through the second embodiment inthis paragraph wherein the top selective layer surface of the asymmetriccarboxylic acid functional group containing polyimide flat sheet orhollow fiber membrane is soaked in a metal cation aqueous solutioncomprising silver nitrate (AgNO₃) aqueous solution for a sufficient timeto form the facilitated transport membrane comprising metal cationion-exchanged or chelated carboxylic acid functional group containingpolyimide.

A third embodiment of the invention is an olefin/paraffin separationprocess comprising (a) contacting a first surface of a membrane with anolefin/paraffin feed, wherein the membrane comprises a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with silver (I) orcopper (I) cations, (b) causing a permeate to flow through the membraneand from a second surface of the membrane wherein the permeate has ahigher concentration of olefin than the olefin/paraffin feed, and then(c) removing a retentate from the first surface of the membrane whereinthe retentate has a lower concentration of olefin than the permeate andwherein the retentate has a higher concentration of paraffin than thepermeate. An embodiment of the invention is one, any or all of priorembodiments in this paragraph up through the third embodiment in thisparagraph wherein the permeate comprises 99.5 mass percent olefin. Anembodiment of the invention is one, any or all of prior embodiments inthis paragraph up through the third embodiment in this paragraph whereinthe facilitated transport membrane comprises a carboxylic acidfunctional group containing polyimide wherein the carboxylic acidfunctional groups are ion-exchanged or chelated with silver (I) orcopper (I) cations wherein the silver (I) or copper (I) cationion-exchanged or chelated carboxylic acid functional group containingpolyimide comprises a plurality of repeating units of formula (I)

wherein X₁ and X₂ are selected from the group consisting of

and mixtures thereof, wherein X1 and X2 may be the same or differentfrom each other; wherein Y₁—COOM is selected from the group consistingof

and mixtures thereof and wherein M is selected from a silver cation or acopper (I) cation;wherein Y2 is selected from the group consisting of

and mixtures thereof, —R′— is selected from the group consisting of

and mixtures thereof, —R″— is selected from the group consisting of —H,COCH₃, and mixtures thereof, M is selected from a silver cation or acopper (I) cation; wherein n and m are independent integers from 2 to500; and wherein n/m is in a range of 1:0 to 1:10.

Without further elaboration, it is believed that using the precedingdescription that one skilled in the art can utilize the presentinvention to its fullest extent and easily ascertain the essentialcharacteristics of this invention, without departing from the spirit andscope thereof, to make various changes and modifications of theinvention and to adapt it to various usages and conditions. Thepreceding preferred specific embodiments are, therefore, to be construedas merely illustrative, and not limiting the remainder of the disclosurein any way whatsoever, and that it is intended to cover variousmodifications and equivalent arrangements included within the scope ofthe appended claims.

In the foregoing, all temperatures are set forth in degrees Celsius and,all parts and percentages are by weight, unless otherwise indicated.

The invention claimed is:
 1. A facilitated transport membrane comprisinga carboxylic acid functional group containing polyimide wherein thecarboxylic acid functional groups are ion-exchanged or chelated withsilver (I) or copper (I) cations wherein the silver (I) or copper (I)cation ion-exchanged or chelated carboxylic acid functional groupcontaining polyimide comprises a plurality of repeating units of formula(I)

wherein X₁ and X₂ are selected from the group consisting of

and mixtures thereof, wherein X1 and X2 may be the same or differentfrom each other; wherein Y₁-COOM is selected from the group consistingof

and mixtures thereof and wherein M is selected from a silver (I) cationor a copper (I) cation; wherein Y2 is selected from the group consistingof

and mixtures thereof, —R′— is selected from the group consisting of

and mixtures thereof, —R″— is selected from the group consisting of —H,COCH₃, and mixtures thereof, M is selected from a silver (I) cation or acopper (I) cation; wherein n and m are independent integers from 2 to500; and wherein n/m is in a range of 1:0 to 1:10.
 2. The facilitatedtransport membrane of claim 1 wherein X₁ and X₂ are selected from thegroup consisting of

and mixtures thereof.
 3. The facilitated transport membrane of claim 1,wherein Y1-COOM is selected from the group consisting of

and mixtures thereof.
 4. The facilitated transport membrane of claim 1wherein Y2 is selected from the group consisting of

and mixtures thereof.
 5. The facilitated transport membrane of claim 1wherein —R″— is selected from the group consisting of —H, COCH₃, andmixtures thereof.